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Appendix   VL

;hew that the rotation is again unstable at higher velocities, and
iigher critical speeds have been discovered, thus :

Critical speeds
	ISt
	2nd
	^rd
	4th


	
	
	
	

Unloaded shaft . . .
	N
	2N
	AN
	8N


	
	
	
	

Concentrated load ...
	N
	2|N
	4|N  .
	io|N

Distributed load ..... .
	N
	2jN
	SiN
	"l2jN


	
	4:
	
	

So, although the de Laval flexible shaft settles down at N, it
would appear to reach the 3rd or 4th speed when at its maximum
rotation. After once passing N the vibrations ;are considerably
reduced between the critical points, the shaft centre line having
two loops at the second, and three loops %at the third speeds.
Referring again to Fig. 1031, the wheel speed is now reduced by
helical gearing N p, constructed in hard steel to meet the peripheral
velocity of 1000 ft. per sec., and the revolutions of the second
shaft Q are proportionally decreased, so as to drive the pulley R.
The wheel, shewn in section at FI? is carefully designed as to
thickness so as to meet the high centrifugal stresses, which are
very great, and practically forbid large wheels, or powers much
beyond 300 H.P. The shaft d is pinned to bush u at its centre
to preserve flexibility, while the blades x T are pressed into the
wheel laterally and then caulked. On the right of shaft Q is a
disc and boss a a, on which are pivoted the governor weights b b,
which, taking the dotted positions on increased speed, press the
spindle c c rightward against the spring, and move lever d d. This
acts on e and c to depress D and throttle the steam. The follow-
ing are some general dimensions :

DE LAVAL TURBINES.

H.P.
	Wheel Dia."
	Revs, per m.
	Rim vel. ft. per sec.
	Shaft dia."

5
	. 4
	30,000
	515
	

3
	8J
	2O,ooo
	774
	

100
	19 J
	13,000
	1115
	I

300
	30          1     10,600
		1378
	iTV